Friction clutch having protective internal shield

ABSTRACT

A frictional clutch for a motor vehicle includes a cover, a pressure plate, a biasing member, an adjustment mechanism and an annular shield. The cover has an axis of rotation. The pressure plate is coupled to the cover for rotation therewith about the axis. The pressure plate has a frictional engagement surface substantially normal to the axis. The biasing member is interposed between the cover the pressure plate, and biases the pressure plate toward an engaged pressure plate position. The adjustment mechanism is centered about the axis and is located at a first radial distance from the axis. The adjustment mechanism is operably disposed between the biasing member and one of the pressure plate and the cover. The annular shield is disposed radially within the adjustment mechanism. The annular shield is axially alignment with the adjustment mechanism. The shield is sized and oriented to protect the adjustment mechanism from debris radiating outward from a central area of the clutch.

FIELD OF THE INVENTION

This invention relates to the field of friction clutches and moreparticularly to friction clutches having adjustment mechanisms.

BACKGROUND OF THE INVENTION

Known friction clutches provide a releasable torsional connectionbetween a motor vehicle engine flywheel and an associated transmission.Repeated clutch disengagement and engagement cycles wear the frictionmaterial of the clutch driven disc. The wear results in a change in theaxial location of the pressure plate in the engagement position. Theshift in axial location results in a decrease in the clutch engagementforce or clamping load. Clutches are commonly provided with adjustmentmechanisms to compensate for such wear.

Clutches achieve the required clamping loads by applying a spring loadto the pressure plate. One type of clutch applies a spring load to aplurality of radially oriented levers which in turn engage the pressureplate. If compressive coil or angle springs are employed, the springload is commonly applied to radially inner ends of the levers. Thelevers are pivotally supported at the radially outer ends. As thefriction material wears, the engaged position of the radially innerlever tips moves closer to the flywheel. Adjustment mechanisms disposedbetween the cover and the levers compensate for this change byincreasing the axial distance of the levers' pivot points from thecover. Alternatively, the change in friction material thickness iscompensated for by providing an adjustment mechanism on the pressureplate instead of the cover. Clutches may employ diaphragm springs inplace of coil springs. Some types of diaphragm springs may have radiallyinwardly directed fingers in place of multiple piece lever and springarrangements. The fingers act as the levers of the heavy duty clutchesin that they are axially displaced at their radially inner most tip torelease the clutch.

Known adjustment mechanisms typically rely on the relative rotation oftwo parts having inclined surfaces in common engagement with each other.The relative rotation of these elements compensates for wear of thefriction material. One strategy for compensating is to axially displacethe pivot ends of the levers away from the cover and closer to theflywheel, thereby reducing the amount of spring deflection required toachieve a full clutch engagement. Another strategy is to axiallydisplace the pressure plate's point of contact with the levers away froman engagement surface of the pressure plate, thereby compensating forfriction material wear. The ease of adjustment is greatly affected bythe coefficient of friction between the relatively rotating parts. Whenthe engaged surfaces become contaminated by debris from the clutch, itincreases the difficulty of properly adjusting the clutch to compensatefor any wear of the friction elements. The configuration of the clutchallows, and indeed promotes the circulation of debris through theclutch. Spinning the clutch cenfrigually forces or impels air andairborne debris through large openings in the clutch cover. Debris mayinclude facing dust, cast iron dust, fretting material and external roaddirt, moisture and/or salt.

It is desired to provide a clutch with an adjusting mechanism which isrelatively insensitive to the debris commonly found in clutches.

It is also desired to provide a clutch with a shield protecting theadjustment mechanism from the entry of debris there into.

SUMMARY OF THE INVENTION

A frictional clutch for a motor vehicle includes a cover, a pressureplate, a biasing member, an adjustment mechanism and an annular shield.The cover has an axis of rotation. The pressure plate is coupled to thecover for rotation therewith about the axis. The pressure plate has africtional engagement surface substantially normal to the axis. Thebiasing member is interposed between the cover the pressure plate, andbiases the pressure plate toward an engaged pressure plate position. Theadjustment mechanism is centered about the axis and is located at afirst radial distance from the axis. The adjustment mechanism isoperably disposed between the biasing member and one of the pressureplate and the cover. The annular shield is disposed radially within theadjustment mechanism. The annular shield is axially alignment with theadjustment mechanism. The shield is sized and oriented to protect theadjustment mechanism from debris radiating outward from a central areaof the clutch.

A frictional clutch for a motor vehicle includes a cover, a pressureplate, an adjusting ring, an adjustment mechanism, a plurality oflevers, a retainer, a plurality of springs and a substantially annularshield. The cover has an axis of rotation. The pressure plate is coupledto the cover for rotation therewith about the axis. The pressure platehas a frictional engagement surface substantially normal to the axis.The adjusting ring is adjustably mounted to the cover and defines aplurality of pivot points. The adjusting ring is centered about theaxis. The adjustment mechanism is axially disposed between the adjustingring and the cover. The adjustment mechanism has inclined surfacesengaging each other. Relative rotation between the first and secondinclined surfaces axially displaces the adjusting ring pivot points awayfrom the cover. The adjustment mechanism is located at a first radialdistance from the axis. The levers are radially oriented about the axis.The levers engage the adjusting ring proximate to a radially outer endof the levers and engage the pressure point radially inwardly of theradially outer end. The retainer is engaged by the radially inner tipsof the levers and is selectively axially moveable between engaged anddisengaged positions. The springs are disposed between the cover and theretainer. The springs bias the levers toward the pressure plate and thesprings act on the levers to bias the pressure plate to an engagedpressure plate position. The shield is disposed radially within theadjustment mechanism, and is in axial alignment therewith. The shieldprotects the adjustment mechanism by blocking debris radiating outwardfrom a central area of the clutch.

The inventive clutch provides an adjusting mechanism which is relativelyinsensitive to the debris commonly found in clutches.

The inventive clutch includes a shield protecting the adjustmentmechanism from the entry of debris there into.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of a first embodiment of the invention.

FIG. 2 is a partial sectional side view of a second embodiment of theinvention.

FIG. 3 is a partial sectional view of a third embodiment of theinvention.

FIG. 4 is a sectional view of a stamped cover illustrating a fourthembodiment of the invention.

FIG. 5 is a partial sectional side view of a fifth embodiment of theinvention.

FIG. 6 is a sectional side view of a sixth embodiment of the invention.

FIG. 7 is an end view of the clutch of FIG. 6 in the direction of arrow7.

FIG. 8 is a schematic view of cams of the clutch of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

A frictional clutch 10 for a motor vehicle is shown in FIG. 1. Clutch 10rotates about an axis 12. A flywheel 14 is rotatably fixed to acrankshaft of a motor vehicle engine (not shown). A driven disc 16,centered with respect to axis 12, has a hub which engages an input shaft17. A friction element 18 of driven disc 16 is engaged by an engagementsurface 20 of pressure plate 22 on one side and by an engagement surface24 of flywheel 14 on the other side.

A cast cover 26 is disposed over pressure plate 22 and is fixed toflywheel 14. A plurality of straps 28 circumferentially extend betweenpressure plate 22 and cover 26. Straps 28 rotatably fix pressure plate22 to cover 26, while allowing relative axial displacement of pressureplate 22 to cover 26. Six levers 30 extend radially outwardly from arelease assembly 34 to an adjustment mechanism 32. Levers 30 engagepressure plate 22 at a point between their engagement with adjustmentmechanism 32 and release assembly 34. The radially innermost tips oflevers 30 engage release sleeve retainer 36. As release assembly 34 isaxially displaced along axis 12, levers 30 pivot about their radiallyouter ends to enable engagement and disengagement of clutch 10. Clutchapply springs 38 are disposed between release sleeve retainer 36 andcover 26, as are assist springs 40. Apply springs 38 bias retainer 36toward flywheel 14. The force of springs 38 is transferred throughlevers 30 to pressure plate 22, thereby clamping driven disc 16 againstengagement surface 24 of flywheel 14.

Adjustment mechanism 32 includes an adjusting ring 42 having engagementprojections 44 retaining levers 30. Adjustment mechanism 32 alsoincludes a first or stationary cam rotatably coupled to adjusting ring44, and a second or rotating cam 48 axially disposed between first cam46 and cover 26. Second cam 48 has a wear indicator tab which extendsthrough a slot in cover 26. First cam 46 and second cam 48 have engaginginclined or cam surfaces which vary the distance of adjusting ring 42from cover 26 with the amount of relative rotation between cams 46 and48. Cams 46 and 48 are shown schematically in FIG. 8. A biasing spring,disposed between second cam 48 and any of the elements not rotating withrespect to cover 26, biases second cam 48 to rotate in a directionincreasing the distance of adjusting ring 42 from cover 26. Although nobiasing spring is shown in FIG. 1, biasing springs 168, 268 and 468 areshown in the embodiments of FIGS. 2, 3 and 5. Adjustment for the wear ofdriven disc 16 occurs when clutch 10 is in a released condition.

While the apply springs 38 engage retainer 36, levers 30 are subject toa reactive load at adjusting ring 42 which is proportional to the loadfrom springs 38. Therefore, adjusting mechanism 32 is operably disposedbetween cover 26 and springs 38.

A rigid adjustment mechanism shield 50 axially extends from cover 26toward pressure plate 22, axially overlapping adjusting ring 42. Shield50 is substantially annular in shape and is located radially withinadjustment mechanism 32. Shield 50 is axially aligned with adjustmentmechanism 32 to overlap and extend beyond the cam surfaces of first cam46 and second cam 48. Shield 50, as shown in FIG. 1, is formed of sheetmetal and has a radially extending flange welded to cast cover 26.However, it should be appreciated that shield 50 may be alternativelyformed, such as by casting it as part of a unitary or one piece shieldand cover. Shield 50 may, if necessary, have a gap or an opening thereinto accommodate passage of an end of the biasing spring on a first sideof shield 50 to the rotatable cam 48 on an opposite side of shield 50.It should also be appreciated that while shield 50 is shown concentricwith axis 12, it may be located eccentrically thereto as necessary todynamically balance clutch 10.

When clutch 10 is in operation, shield 50 prevents debris such as facingdust, cast iron dust, fretting material and external road dirt, moistureand salt from being centrifugally flung outward and into the cam orinclined surface interface from the center of the clutch. This debris,when it accumulates between the surface interface, has a deleteriouseffect on the performance of the adjustment mechanism. Shield 50advantageously reduces the amount of debris reaching the interface. Theaxial length of shield 50 is selected to insure overlap of shield 50over the cam surfaces.

A second embodiment of a shield for a clutch adjustment mechanism isshown in FIG. 2. Clutch 110 has a stamped cover 126 instead of the castcover of the first embodiment. Clutch 110 is shown without a flywheeland without a driven disc. Pressure plate 122 is rotatably connected tocover 126 by a plurality of straps (not shown). The straps, like straps28, prevent relative rotation between pressure plate 122 and cover 126while allowing relative axial displacement of pressure plate 122relative to cover 126. A flexible shield 150 extends between a radiallyinwardly projecting engagement shelf 152 of adjusting ring 144 to arearmost inner surface of cover 126 to provide a protective seal inaxial alignment with both first cam 146 and second cam 148. Flexibleshield 150 has folds which enable accordion style deflection asadjusting ring 144 is moved further from cover 126 with increasing wearof the driven disc.

It should be appreciated that bolt 154 is typically removed from clutch110 after installation of clutch 110 in a vehicle to enable pressureplate 122 to travel freely. Flexible shield 150 is formed of a suitableplastic which is both able to flex, and to sustain the anticipatedtemperature conditions of clutch 110.

A third embodiment of the invention, shown in FIG. 3, is substantiallylike that of the second embodiment shown in FIG. 2. However, in place ofa unitary shield 50 or 150, shield 250 comprises a first baffle element256 extending into a baffle slot 258. Baffle slot 258 is defined on oneside by second cam 248 and on the opposite side by a second baffleelement 260 extending toward adjusting ring 144. Shield 250 defined bybaffle elements 256 and 260 greatly reduce the amount of debris which isable to reach the cam surfaces.

FIG. 4 shows a stamped cover 326. Cover 326 has a stamped one pieceshield 350 fixed thereto. Shield 350 is substantially the same as shield50, except that shield 350 is associated with a stamped cover 326instead of a cast cover 26.

FIG. 5 illustrates a clutch 410 nearly identical to the clutch 210 ofFIG. 3. However, shield 450 employs a first baffle element 456 extendingfrom adjusting ring 444 instead of first cam 446. However, as in theclutch of FIG. 3, first baffle element 456 extends into a baffle slot458 and second baffle element 460 extends from second cam 448 towardadjusting ring 444.

A clutch 510 having an alternative adjustment mechanism 532 is shown inFIGS. 6 and 7. Clutch 510 uses, in place of cams, outer diameter threads562 on an outer diameter of adjusting ring 544 and inner diameterthreads 564 in cover 526. Threads 562 and 564 each provide respectiveinclined surfaces which result in the axial displacement of adjustingring 554 with relative rotation between those surfaces. In theembodiment shown in the FIGS. 6 and 7, adjustment does not occurautomatically. Adjustment is made by rotating a pinion gear 566 whichengages teeth on an inside diameter of adjusting ring 544 in a mannerwell known in the art. It should be appreciated that it is also knownemploy a spring loaded worm gear in place of pinion gear 566 for anautomatic wear compensating system. Most commonly, the threads used insuch adjustment mechanisms are of a fine thread. The coarse or acmestyle thread shown in the figures has been found to be much lesssensitive to the intrusion of debris than fine threads. With finethreads, the debris tends to induce corrosion and binding of thethreads, rendering the adjustment mechanism ineffective. It has beenfound that the increase in the helix angle of the thread, associatedwith the switch to coarse threads, reduces any tendency of the threadsto bind. It has been further found that torsional activity created bythe engine, combined with the relatively coarse thread and theassociated large helix angle, keeps the adjusting ring operating in afree condition for a longer period of time than an adjustment mechanismemploying a fine thread. The benefits of coarse threads can be furtherenhanced by shielding the threaded area from debris with a shield 550which axially extends from cover 526 toward pressure plate 522 at leastas far as the threaded interface.

It should be appreciated that there are readily apparent alternativeembodiments to the above-described clutch configurations. For example, adiaphragm spring may be used in place of the coil springs. Yetalternatively, a diaphragm spring with integral levers or fingers couldbe employed in place of the separate springs and levers. Additionally,the adjustment mechanism and the associated shield could bealternatively disposed between the levers and the pressure plate insteadof between the levers and the cover. Also, the locations of the rotatingcam and the stationary cam could be transposed.

The embodiments disclosed herein have been discussed for the purpose offamiliarizing the reader with the novel aspects of the invention.Although preferred embodiments of the invention have been shown anddisclosed, many changes, modifications and substitutions may be made byone having ordinary skill in the art without necessarily departing fromthe spirit and scope of the invention as described in the followingclaims.

We claim:
 1. A friction clutch for a motor vehicle comprising:a coverhaving an axis of rotation; a pressure plate coupled to the cover forrotation therewith about the axis and having a frictional engagementsurface substantially normal to the axis; a biasing member acting on alever interposed between the cover and the pressure plate and biasingthe pressure plate toward an engaged pressure plate position; anadjustment mechanism centered about the axis and located at a firstradial distance from the axis operably disposed between the lever andone of the pressure plate and the cover; and a substantially annularshield disposed radially within and axially overlapping the adjustmentmechanism immediately adjacent the adjustment mechanism, wherein theshield is sized and oriented to protect the adjustment mechanism fromdebris radiating outward from a center area of the clutch.
 2. Africtional clutch as claimed in claim 1, wherein the shield is flexibleand is formed of plastic and is formed separate from the cover.
 3. Africtional clutch as claimed in claim 2, wherein the shield abuts thecover on a first end and engages the adjusting mechanism on a secondend, sealingly enclosing incline surfaces of the adjustment mechanism.4. A frictional clutch as claimed in claim 1, wherein the shield iscomprised of overlapping baffle elements.
 5. A frictional clutch asclaimed in claim 1, wherein the shield is rigid and axially extends fromthe cover toward the pressure plate.
 6. A frictional clutch as claimedin claim 1, wherein the adjustment mechanism comprises mating threads onthe cover and a portion of the adjustment mechanism.
 7. A frictionalclutch as claimed in claim 1, wherein the adjustment mechanism comprisesmating acme threads on the cover and a portion of the adjustmentmechanism.
 8. A frictional clutch for a motor vehicle comprising:a coverhaving an axis of rotation; pressure plate coupled to the cover forrotation therewith about the axis and having a frictional engagementsurface substantially normal to the axis; an adjustment ring adjustablymounted to the cover and defining a plurality of pivot points andcentered about the axis; an adjustment mechanism axially disposedbetween the adjusting ring and the cover and having first and secondinclined surfaces engaging each other wherein relative rotation betweenthe first and second inclined surfaces axially displaced the adjustingring pivot points away from the cover and the adjustment mechanism beinglocated at a first radial distance about the axis; a plurality of leversradially oriented about the axis and engaging the adjusting ringproximate to a radially outer end of the levers and engaging thepressure plate radially inwardly of the radially outer end; a retainerengaged by the radially inner tips of the levers and selectively axiallymoveable between engaged and disengaged positions; a plurality ofsprings disposed between the cover and the retainer wherein the springsbias the lever toward the pressure plate and the springs act on thelevers to bias the pressure plate to an engaged position; and asubstantially annular shield disposed radially within the adjustmentmechanism and in axial alignment therewith immediately adjacent theadjustment mechanism, wherein the shield protects the adjustmentmechanism by blocking debris radiating outward from a center area of theclutch.
 9. A friction clutch as claimed in claim 8, wherein the shieldis flexible and is formed of plastic.
 10. A frictional clutch as claimedin claim 9, wherein the shield abuts the cover and extends axially fromthe cover and sealingly engages the adjusting ring and sealinglyencloses the inclined surfaces of the adjustment mechanism.
 11. Africtional clutch as claimed in claim 8, wherein the shield comprisesoverlapping baffle elements.
 12. A frictional clutch as claimed in claim8, wherein the shield is rigid and axially extends from the cover towardthe pressure plate.
 13. A frictional clutch as claimed in claim 8,wherein the adjustment mechanism comprises outer threads on theadjusting ring and mating inner acme threads in the cover.
 14. Africtional clutch as claimed in claim 8, wherein the adjustmentmechanism comprises outer acme threads on the adjusting ring and matinginner acme threads in the cover.
 15. A frictional clutch for a motorvehicle comprising:a cover having an axis of rotation; a pressure platecoupled to the cover for rotation therewith about the axis and having africtional engagement surface substantially normal to the axis; meansfor biasing the pressure plate away from the cover disposed between thepressure plate and the cover; means for adjusting a load applied to thepressure plate by the biasing means, the adjusting means being disposedbetween the biasing means and one of the pressure plate and the cover;and a substantially annular shield disposed within the cover andradially within the adjusting means in axially alignment therewith,wherein the shield is sized and oriented to protect the adjusting meansfrom debris radiating outward from a center area of the clutch.